The chemical oxygen iodine laser works by generating excited oxygen gas through a chemical process, transporting this excited gas to a laser cavity where it mixes with molecular iodine, dissociates the iodine into atoms and transfers its energy into the iodine atoms. Spontaneously emitted photons, in conjunction with an optical cavity, stimulate the emission of light from the iodine atoms in a coherent beam. De-excited atoms are re-excited through collisions with the excited oxygen. The cycle of exciting, stimulating and de-exciting the iodine atoms continues until energy in the oxygen reservoir is depleted down to some threshold value determined by the temperature of the medium In the chemical oxygen iodine laser the chemically generated, excited oxygen is the energy source for the laser and the iodine is the means for converting the stored energy to laser light.
Gas phase, diatomic, molecular oxygen is capable of existing in a number of different energy states. The lowest energy state is termed the ground state and denoted O2 (X3xcexa3). The first excited state, O2 (a1xcex94), exists approximately 1 electron-volt above the ground state and is the state of oxygen which stores energy for use in the chemical oxygen iodine laser. The second excited state, O2 (b1xcexa3), exists about 1.6 electron-volts above the ground state and has been created by the collision of two O2 (a1xcex94) molecules. Therefore, the formation of this species represents a loss mechanism affecting the efficiency of the laser.
To power a chemical oxygen iodine laser, O2 (a1xcex94) has to be created in large densities and large ratios relative to the O2 (X3xcexa3) ground state oxygen. The primary process used to create O2 (a1xcex94) in the percentage and density to power a laser has been the reaction of a halogen gas with a liquid mixture of an alkali hydroxide and hydrogen peroxide. This chemical process has been the basis for numerous chemical generator designs since 1977.
Optical sources and detectors have been used to study oxygen and its first two excited states since 1933. In some cases lasers have been used to optically excite ground state oxygen, O2 (X3xcexa3), to its second electronically excited state, O2 (b1xcexa3) for the purpose of studying its properties and deactivation mechanisms. Optical transitions induced by laser light or any light source are rather difficult to achieve because of the low cross-section for interaction between the light and the molecule. The transition to this state is therefore termed xe2x80x9cnot allowed.xe2x80x9d Reactions of various gas species like O2, CO, HBr, etc. with this state of oxygen have been found to deactivate the O2 (b1xcexa3) to O2 (a1xcex94) with 100% efficiency. Additionally collisions with walls made of glass and stainless steel have also shown this preferential deactivation channel to O2 (a1xcex94). In part this deactivation process explains why the formation of O2 (b1xcexa3) in the laser is not as serious a loss mechanism, since same of the energy is recovered through its deactivation.
The advances over the last ten years in semiconductor and solid state lasers have presented industry with a wide range of tools for use in optically triggered processes. In the present case, to excite significant fractions of oxygen at high density to the O2 (b1xcexa3) state requires the use of specially tailored, high intensity, narrow-band light sources. Three types of sources meet the minimum requirements for generating sufficient excited oxygen densities to support laser output from an oxygen iodine medium. These are solid state lasers (Ti:sapphire and Alexandrite); diode lasers (including InGaAsP and GaASP-AlGaAS tensile-strained quantum well lasers); and fiber lasers (doubled, Erbium doped fiber lasers).
The present invention overcomes the problem of the use of toxic and explosive chemicals in the generation of excited oxygen for the chemical oxygen iodine laser. Additionally it provides a clean source and high flow rate of excited oxygen for use in other potential laser systems. An electric-optical generation process, yielding high fractions of excited oxygen, replaces the chemical generation process for excited oxygen in the chemical oxygen laser.
Light is generated from electric laser sources and coupled into a cold oxygen gas flow, producing large fractions of the oxygen in the second excited electronic state. Since the light is rather wealdy absorbed on a per unit length basis optics are used to multi-pass the incident beam through the medium until greater than 90% of the light is absorbed. Combination of the wall collisions and gas phase collisions deactivate the oxygen from its second excited state to its first excited state the singlet delta state. Incident continuous light fluences of 50-100 kw/cm2, oxygen gas pressures of 30 torr-70 torr, oxygen gas temperatures of 100 K-150 K, absorption lengths of 10 meters-15 meters and flow velocities of 10 meters/s yield a greater than 40% fraction of the flow in the desired excited state of oxygen. Wall collisions or the addition of about 0.1 torr of HBr efficiently deactivates the singlet sigma to singlet delta in the required time frame.